# Re: \[PATCH 1/5\] KVM: rseq: Update rseq when processing NOTIFY\_RESUME on xfer to KVM guest

- From: Paolo Bonzini \<pbonzini@redhat.com\>
- Date: 2021-09-06 10:28:23 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2021/09/1498215
- Thread: https://ratatoskr.run/linux-arm-kernel/2021/08/1480992/t.md

```text
On 20/08/21 20:51, Mathieu Desnoyers wrote:
>> Ah, or is it the case that rseq_cs is non-NULL if and only if userspace is in an
>> rseq critical section, and because syscalls in critical sections are illegal, by
>> definition clearing rseq_cs is a nop unless userspace is misbehaving.
> Not quite, as I described above. But we want it to stay set so the CONFIG_DEBUG_RSEQ
> code executed when returning from ioctl to userspace will be able to validate that
> it is not nested within a rseq critical section.
>
>> If that's true, what about explicitly checking that at NOTIFY_RESUME?  Or is it
>> not worth the extra code to detect an error that will likely be caught anyways?
> The error will indeed already be caught on return from ioctl to userspace, so I
> don't see any added value in duplicating this check.

Sean, can you send a v2 (even for this patch only would be okay)?

Thanks,

Paolo

```